Bottom-Up Construction of a CO2-Based Cycle for the Photocarbonylation of Benzene, Promoted by a Rhodium(I) Pincer Complex

Article abstract of DOI:10.1021/jacs.6b05128

The use of carbon dioxide for synthetic applications presents a major goal in modern homogeneous catalysis. Rhodium-hydride PNP pincer complex 1 is shown to add CO₂ in two disparate pathways: one is the expected insertion of CO₂ into the metal-hydride bond, and the other leads to reductive cleavage of CO₂, involving metal-ligand cooperation. The resultant rhodium-carbonyl complex was found to be photoactive, enabling the activation of benzene and formation of a new benzoyl complex. Organometallic intermediate species were observed and characterized by NMR spectroscopy and X-ray crystallography. Based on the series of individual transformations, a sequence for the photocarbonylation of benzene using CO₂ as the feedstock was constructed and demonstrated for the production of benzaldehyde from benzene.

Full text of DOI:10.1021/jacs.6b05128

Subscriber access provided by La Trobe University Library
Article
Bottom-Up Construction of a CO2-Based Cycle for the Photocarbonylation
of Benzene Promoted by a Rhodium(I) Pincer Complex
Aviel Anaby, Moran Feller, Yehoshoa Ben-David, Gregory Leitus,
Yael Diskin-Posner, Linda J.W. Shimon, and David Milstein
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b05128 • Publication Date (Web): 11 Jul 2016
Downloaded from http://pubs.acs.org on July 11, 2016
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 12
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
Bottom-Up Construction of a CO2-Based Cycle for the Photo-
carbonylation of Benzene Promoted by a Rhodium(I) Pincer
Complex.
Aviel Anaby, † Moran Feller, † Yehoshoa Ben-David, † Gregory Leitus, ‡ Yael Diskin-Posner, ‡ Lin-
da J. W. Shimon, ‡ and David Milstein†*
9
†Department of Organic Chemistry and ‡Department of Chemical Research Support, Weizmann Institute of Science,
Rehovot 76100, Israel.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ABSTRACT: The use of CO2 for synthetic applications presents a major goal in modern homogenous catalysis. Rhodium–
hydride PNP pincer complex 1 is shown to add CO2 in two disparate pathways. One is the expected insertion of CO2 into
the metal–hydride bond, and the second pathway leads to reductive cleavage of CO2, involving metal–ligand-cooperation.
The resultant rhodium–carbonyl complex was found to be photoactive, enabling the activation of benzene and formation
of a new benzoyl complex. Organometallic intermediate species were observed and characterized by NMR spectroscopy
and X-ray crystallography. Based on the series of individual transformations, a sequence for the photocarbonylation of
benzene using CO2 as the feedstock was constructed, and demonstrated for the production of benzaldehyde from ben-
zene.
ther efficient rhodium catalysts for the hydrogenation of
CO2 have been reported by Leitner et al. and others,
INTRODUCTION
achieving good turnover numbers (TON) under mild
conditions.24,30 The insertion process of CO2 into the Rh–
H bond of model Rh(I) and Rh(III) complexes is well
studied.22b,22d,24c,38 It has been suggested that, while for
Rh(I) complexes CO2 insertion to afford a formate com-
plex is facile, elimination of the formate product is rate
limiting; whereas for Rh(III) complexes the actual inser-
tion of CO2 into the Rh–H bond is rate determining.39
Chirik et al. demonstrated the facile insertion of CO2 into
CO2 presents an appealing one-carbon synthon for the
chemical industry, and its direct incorporation into com-
plex molecules is highly desireble.1–6 It is thermodynami-
cally challenging to reduce CO2 in a clean and useful
manner.2d,6c,7 Reductive ‘splitting’ or cleavage of CO2 is
possible, either involving oxygen transfer,2b,8–15 dispropor-
tionation to carbonates,8,16,17 or, more commonly, to car-
bon monoxide and water, in the reverse water–gas–shift
reaction (r-WGSR).1b,18–20 An efficient and selective pro-
cess for CO2 splitting to CO and water is highly beneficent
towards CO2 utilization as a viable synthon.1b,1c,3,4,6c,7,21a The
use of hydrogen as the reducing agent is an atom efficient
means to convert CO2 into useful compounds.21b–d For
several decades, many organometallic complexes have
been suggested as potential homogenous catalysts for the
reduction of CO2 by hydrogen. Within this context, the
insertion reaction of CO2 into metal–hydride bonds has
been the focus of many studies. While in some cases it
has been implied that a nucleophilic attack of the hydride
on the CO2 carbon initiated the insertion,22 it has been
largely accepted to follow π-coordination of the CO2 to
the metal center, and subsequent σ-bond metathesis to
afford a formate ligand.6c,18b,21a,21b,23 Consequently, homog-
enous hydrogenation of CO2 to formic acid (or salts
thereof) has been achieved using metal complexes as
catalysts.23d,24–31 Moreover, since this process is reversible,
formic acid has been proposed as a potential hydrogen
chemical storage system.21c,26c,32–34 Most outstanding are
the highly efficient iridium catalyzed hydrogenation of
CO2 reported by Nozaki et al.,26a,35 as well as the relatively
benign iron catalyzed CO2 hydrogenation.26b,27 Alterna-
tively, products of carbon-dioxide hydrogenation, includ-
ing methanol14,21d,32a,36 and formic acid, may be useful as
reagents in further chemical transformations.6b,6e,11,37 Ra-
the Co–H bond of
a
PNP (2,6-bis(di-tert-butyl-
phosphinomethyl)pyridine) pincer complex, resulting in a
stable formate complex.19 The catalytic hydrosilylation of
CO2 was demonstrated by Chirik et al., albeit hampered
by the eventual formation of the corresponding cobalt–
carbonyl complex, likely as result of CO2 cleavage under
the reaction conditions.19
In the past decade, our group has studied metal–ligand-
cooperation (MLC)40 in activation of substrates such as
alcohols,41 amines,42 nitriles,43 boranes,44 dihydrogen,45–47
and dioxygen.48 Relying on the potential of pyridine-
based pincer complexes to undergo aromatization–
dearomatization cycles, a novel mode of chemical bond
activation was discovered, leading to efficient and benign
catalytic transformation, most useful in hydrogenation,
and dehydrogenation reactions.40b–c,49 The interaction of
pincer complexes with CO2 was shown, in some cases, to
entail the addition of CO2 to the dearomatized ligand
backbone, when the π-acidic carbon of CO2 resides on the
pincer ligand benzylic position.29a,50 Recently our group
has observed that in the case of an iridium–hydride PNP
complex, CO2 is incorporated at the ligand benzylic posi-
tion as a resting state, but is subsequently protonated via
MLC and cleaved at the metal center to afford water and a
CO ligand.51
ACS Paragon Plus Environment

Journal of the American Chemical Society
Here we report on a pincer Rh(I)–H promoted splitting of
CO2 by MLC, leading to a dearomatized Rh(I) carbonyl
complex which, upon UV irradiation, C–H activates ben-
zene. Protonation of the resulting benzoyl complex leads
to benzaldehyde (Scheme 1). Deprotonation and hydro-
genation of the rhodium complex closes a novel MLC-
promoted stoichiometric cycle, which can be repeated
consecutively, for the formation of benzaldehyde from
CO2 and benzene.
Page 2 of 12
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
RESULTS AND DISCUSSION
Carbon dioxide reacts instantly at room temperature with
the (PNP)RhH complex
1
(PNP
-
2,6-bis(di-tert-
butylphosphinomethyl)pyridine).46 Upon addition of one
equiv, or more, of CO2 gas to complex 1 in THF, the im-
mediate product observed by NMR spectroscopy is the
formate complex 2 (Scheme 1). Complex 2 exhibits a pro-
Figure 1. ORTEP representation of complex 2, with thermal
ellipsoids at 50 % probability. Hydrogen atoms omitted for
clarity. One of two discrete formate geometries in the asym-
metric unit shown. Selected bond lengths [Å] and bond an-
gles [°]: C24–O1, 1.214(4); C24–O2, 1.271(4); O2–Rh1, 2.075(1);
Rh1–O2–C24, 128.0(2); O2–C24–O1, 130.1(3); N1–Rh1–O2,
169.02(6); P1–Rh1–P2, 167.62(2).
1
ton signal in the H-NMR spectrum at 8.6 ppm (double
3
4
triplet, JRhH = 2.8 Hz, JPH = 1.4 Hz) which is consistent
1
with a formyl proton. The symmetric H-NMR pattern of
the ligand backbone, as well as the doublet signal in the
1
31P{1H}-NMR (60 ppm, JRhP = 154 Hz) are indicative of an
Conversion to the carbonyl complex 3 indicates apparent
splitting of the CO2 to CO and water. Water formation
could not be unequivocally asserted, yet it is expected by
stoichiometry, and observed in the analogous CO2 activa-
tion by (PNP)IrH pincer complex.51
aromatized square planar Rh(I) complex.
Scheme 1. CO2 cleavage and photocarbonylation of
benzene
The reaction of complex 1 with CO2 was monitored by
variable temperature NMR spectroscopy, in acetone-d6
(Figure S21 in ESI). Rapid formation of complex 2 oc-
curred even at 200 K. When raising the temperature to
250 K for 90 min, complex 3 was observed to form along-
side
the
cationic
rhodium–carbonyl
complex,
[(PNP)RhCO]+X-, which exhibits a doublet in the 31P{1H}-
NMR at 79.8 ppm (1JRhP = 120.1 Hz). The cationic rhodium
carbonyl complex (with X = BF4, BArf, OC(O)CF3, Cl) was
previously reported by our group.52 Attempts to isolate
and fully characterize this complex resulted in formation
of complex 3. It is plausible that the cationic complex is
4a (Scheme 1), possessing a hydroxide counter anion. Up-
on solvation, or isolation, the basic counter-ion would
deprotonate the benzylic proton of the ligand, yielding
the dearomatized product, complex 3, and water. Com-
plex 4a is observed independently when water is added to
complex 3, with a characteristic 31P{1H}-NMR signal at
X-ray crystallography of crystals of complex 2, obtained
by low temperature crystallization, indicated an η1–
OCHO structure (Figure 1), analogous to that of the co-
balt–formate complex, reported by Chirik et al.19 Van der
Vlugt et al. recently observed a Rh(I)–formate complex as
an intermediate in catalytic formic acid decomposition,34
1
79.4 ppm (d, JRhP = 122 Hz). Complex 4a was only ob-
served as a product of CO2 cleavage when the experiment
was run in polar solvents at low temperatures. The possi-
bility of a bicarbonate formation16,38f is less likely, since in
that case the process is unlikely to be reversible, due to
the bicarbonate anion mild basicity. The ratio between
complexes 4a and 3 in solution was found to be tempera-
ture dependent,53 with complex 4a being the major prod-
uct in solution at lower temperature (1.6 : 1 of 4a / 3 at 220
K) and complex 3 becoming the major species at elevated
temperatures (1 : 1.5 of 4a / 3 at 273 K).
1
although the formate proton H-NMR signal was not re-
ported. Complex 2 is not stable, even at low temperatures,
and cannot be separated from the reaction solution.
When vacuum is applied to a solution containing com-
plex 2, CO2 is extruded and complex 1 re-forms; when
complex 2 is kept in solution, the color slowly changes
from orange to red, and monitoring by NMR spectroscopy
confirms the formation of the dearomatized (PNP*)RhCO
complex 346 (PNP* - deprotonated PNP pincer ligand,
Scheme 1), within 5 hours at room temperature.
Catalytic hydrogenations of CO2 by complex 1 were at-
tempted. Following a similar protocol to that of Leitner et
2
ACS Paragon Plus Environment

Page 3 of 12
Journal of the American Chemical Society
al.,24b–c a 1 : 5 triethylamine / THF solution of complex 1
(0.01 mM) was pressurized to 40 bar of H2 and CO2 (at 1 : 1
Scheme 3. Isotopic labeling experiment
1
2
3
4
5
6
7
8
ratio) and stirred for 20 hours at room temperature. A
turnover number of 23 was observed towards the for-
mation of the triethylammonium salt of formic acid.
When the reaction was repeated without base,29b a TON
of 7 was measured. Analysis of the solutions after reaction
by NMR spectroscopy revealed that, in both cases, com-
plex 1 was consumed and the cationic rhodium–carbonyl
1
complex 4b (31P{1H}-NMR signal at 79.5 ppm, d, JRhP = 120
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Hz) was formed with a formate counter anion (Scheme 2).
Thus, it appears that on the one hand, rhodium complex 1
readily undergoes insertion of CO2 into the metal–hydride
bond, forming the formate complex 2 which may be hy-
drogenated back to complex 1, eliminating formic acid; on
the other hand, CO2 cleavage to form 3 eventually halts
the reaction, stopping efficient hydrogenation of CO2 to
formic acid (Scheme 2).
Notably, when 1 equiv CO2 is added to a water / THF (2 :
3) solution of complex 1, the solution color turns within
seconds from brown to yellow, and NMR spectroscopy
indicates the exclusive formation of the cationic rhodi-
um–carbonyl complex 4a (31P{1H}-NMR signal at 79.5
Scheme 2. Reduction of CO2 by complex 1.
1
ppm, d, JRhP = 120 Hz), which is the product of protona-
tion of complex 3 by water. Complex 2 is not detected at
all in the aqueous solution, and may either have been very
rapidly consumed, or not have formed altogether. The
accelerating effect of water on processes involving metal
ligand cooperation is well documented.51,54
The insertion pathway, leading to the formation of com-
plex 2, matches that of the analogous PNP pincer complex
of cobalt, observed by Chirik et al.19 The second pathway,
resulting in the splitting of CO2, has been observed in our
group as the prevailing outcome of CO2 reaction with the
analogous iridium PNP pincer complex.51 The duality of
rhodium–hydride complex 1 in reaction with CO2 demon-
strates elegantly the trend in reactivity when descending
down the ninth column of the periodic table. Although it
cannot be unequivocally asserted at this point, we believe
the mechanism leading to the formation of complex 3
from complex 1 and CO2 is disparate from the reversible
insertion pathway leading to the formate complex 2.
The insertion of CO2 into the Rh–H bond of complex 1
and rapid formation of complex 2 is, evidently, a reversi-
ble process. As aforementioned, complex 2 reverts to
complex 1 under reduced pressure. A spin saturation
6b,21b,55
Complex 2 is the product of facile insertion of CO2
1
into the metal–hydride bond.19,24a,24c,38a,38d,56 The process
leading to CO2 cleavage is slower and apparently, in our
case, irreversible. As of yet, we could not find compelling
evidence to support a mechanistic pathway for the ob-
served CO2 cleavage (formally, a rWGSR) by complex 1. It
likely follows a similar pathway to that observed for the
analogous iridium complex.51 This may entail an η1–CO2
coordination, forming an elusive and unstable carboxylate
intermediate,1a,8,15,21,55,57 which may then be protonated and
dehydroxylatyed,58 through metal–ligand-cooperation, to
yield a carbonyl ligand (complex 3) and water.51 Alterna-
tively, other mechanistic pathways may be conceived,
such as disproportionation,8,16,38f decarbonylation,19,38b or
dehydration of the formate.32a,58 Formation of complex 3
and water may serve as a thermodynamic sink that drives
the system towards CO2 cleavage rather than formate
formation.
transfer (SST) H-NMR experiment confirmed the chemi-
cal exchange between the hydride of complex 1 and the
formate proton of complex 2 in solution (Figure S20 in
ESI). Moreover, 13C labeled CO2 addition to non-labeled
complex 2 (formed in-situ by addition of 1 equiv CO2 gas
to a THF solution of complex 1) results in formation of the
13C labeled complex 2, and eventually to the 13C labeled
complex 3 (depicted as 2*, and 3*, respectively, Scheme 3).
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
While reductive cleavage of CO2 with no net change in
Page 4 of 12
1
2
3
4
5
6
7
8
the oxidation state of the rhodium metal is remarkable in
itself, the resultant dearomatized monocarbonyl product
complex of this stoichiometric reaction is known to be
quite unreactive.46,52 It was, thus, gratifying to discover
that upon irradiating a benzene solution of the dearoma-
tized monocarbonyl complex 3 under UV(B) (Luzchem
LZC-UVB lamps with peak intensity at 320 nm), gradual
formation of the benzoyl complex 5 is observed. Conver-
sion to complex 5 reaches 50–80% (by NMR spectroscopy)
in solution, after 72 h irradiation (Figure 2). Intermediates
of the carbonylation reaction could not be observed. The
only other products observable by NMR spectroscopy are
the previously reported (PNP)RhPh complex 646,59(15–45%
by integration after 72 h under UV(B)), and residual car-
bonyl complex 3.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. ORTEP representation of complex 5, with thermal
ellipsoids at 50 % probability. Hydrogen atoms omitted for
clarity. One of two identical molecules in the asymmetric
unit shown. Selected bond lengths [Å] and bond angles [°]:
C24–O1, 1.235(2); C24–C25, 1.534(3); C24-Rh1, 1.993(2); Rh1–
C24–O1, 124.7(2); Rh1–C24–C25, 120.9(1); O1–C24–C25,
114.4(2).
Indeed, when the irradiation of a benzene solution of
complex 3 is carried out with minimal headspace over the
solution, that is, the solution occupies nearly the whole
vessel volume, complex 5 is consistently formed in 65%
yield (by NMR, after 72 h irradiation). When a benzene
solution of complex 3 is irradiated under UV(B) in a vessel
with a large headspace volume, rhodium–phenyl complex
6 is formed almost exclusively within a 72 h irradiation
period.
Although a radical mechanism cannot be excluded for the
photocarbonylation reaction,60,61 and while early studies
had suggested the possibility of a dissociative mechanism
(ligand or CO extrusion) to lead to C–H activation;62 ex-
haustive mechanistic research, conducted by Goldman,61
and Field63 on rhodium catalyzed photocarbonylation of
benzene64–66 suggests that it may proceed by an associa-
tive mechanism, whereby UV irradiation excites the rho-
dium carbonyl complex 3, enabling C–H activation of
benzene. In the case of the PNP pincer complex 3, C–H
activation by MLC leads to re-aromatization of the pincer
ligand, which may serve as a driving force for this reac-
tion. The postulated penta-coordinate intermediate
(Scheme 5) would undergo migratory insertion,67 result-
ing in the square planar complex 5. CO loss, evident by
the formation of complex 6, may also be expected to oc-
cur from the suggested penta-coordinate rhodium species
under the reaction conditions.61,65 The main mechanistic
difference in the photocarbonylation of benzene by com-
plex 3, versus that of the Vaska-type rhodium complex-
es,61,63,64a,66 is that benzene activation by the Rh(I) takes
place by metal-ligand cooperation, and hence the prod-
uct is a Rh(I) benzoyl complex (rather than Rh(III)), with
no overall change in the metal oxidation state.
1
Figure 2. H-NMR spectrum (C6D6, 400 MHz) of the result-
ing mixture after irradiation of complex 3 in benzene for 72 h
under UV(B). Signal assignments for complex 5 are in blue.
Inset: 31P{1H}-NMR spectrum (C6D6, 122 MHz) of the corre-
sponding mixture.
The spectral assignment of the benzoyl complex was con-
firmed when complex 5 was synthesized independently
from the dearomatized dinitrogen complex 759 under re-
duced pressure (facilitating ligand exchange) with 1 equiv
benzaldehyde in benzene (Scheme 4). Complex 5 thus
obtained was also crystallized and its structure elucidated
by X-ray crystallography (Figure 3).
Scheme 4. Independent synthesis of complex 5.
The variability in the relative amounts of the benzoyl
complex 5 and the phenyl complex 6 arises from variable
reaction conditions, such as type of vessel, amount and
concentration of solution and ambient temperatures. It
became evident that CO loss during irradiation leads to
increased formation of complex 6, at the expense of com-
plex 5.
4
ACS Paragon Plus Environment

Page 5 of 12
Journal of the American Chemical Society
Scheme 5. Photocarbonylation reaction of complex 3 acids promote the release of free benzaldehyde from
1
2
3
4
5
6
7
8
in benzene.
complex 5, in up to 50% yield. While trifluoromethanesul-
fonic acid, and diphenylacetic acid both enabled the re-
lease of benzaldehyde (Figures S45–S46, ESI), paratol-
uenesulfonic acid (TsOH) was found to be the most suit-
able for this purpose, providing a more ‘well behaved’
system that was convenient to monitor and study. Thus,
upon addition of 1 equiv TsOH to a benzene solution of
complex 5, initially only a slight color change is observed,
from dark brown to a slightly lighter brown solution.
NMR spectroscopy reveals that one major complex is
formed, with a similar 1H-NMR pattern to that of complex
5, and a 31P{1H}-NMR signal at 62 ppm (d, 1JRhP = 117 Hz). In
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
addition, a new hydride signal is observed in the H-NMR
1
2
spectrum (dt, JRhH = 31 Hz, JPH = 11 Hz). These spectral
features indicate a rhodium(III) hydrido-benzoyl-tosylate
complex (complex 8, Scheme 6). The solubility of this
complex in non-polar solvents (even at low tempera-
tures), as well as the hydride chemical shift and the Rh–P
coupling constant all indicate a charge neutral octahedral
rhodium(III) complex, with the TsO- ligand coordinated
(possibly weakly).42c,52 Complex 8 was observed for several
hours in solution at low temperature, however it could
not be isolated. Within an hour at room temperature, the
solution color changes to bright orange and two new ma-
jor complexes are observed by NMR spectroscopy, with
disappearance of complex 8.
A comparison experiment was conducted in parallel, with
two separate J. Young NMR tubes charged with the same
amount and concentrations of complex 3: the one in
C6H6, and the second in C6D6. Both solutions were irradi-
ated for 72 h simultaneously under UV(B). Whereas only
partial conversion was achieved in the deuterated solvent,
with ratios of 13 : 5 : 3 of complexes 3 / 5 / 6 (respectively),
the sample in regular benzene showed full conversion,
with 4 : 1 ratio of complexes 5 / 6 respectively. This result
indicates C–H activation to be the rate limiting step in the
photocarbonylation reaction. Moreover, the splitting of
the corresponding signals in the 31P{1H}-NMR spectrum
(Figure S33, ESI) indicate deuterium incorporation in the
ligand backbone of complex 3 after irradiation in C6D6,
which supports the suggested reversible formation of a
phenyl-carbonyl rhodium intermediate. Complex 5 is also
observed upon addition of CO gas to a solution of com-
plex 6 (Figure S36, ESI). Complex 3 is also formed in this
case, demonstrating both the ease of migratory insertion,
and the reversibility of the carbonylation reaction.68
Scheme 6. Protonation of complex 5 and elimination
of benzaldehyde.
Since the source of the carbonyl group is CO2 (Scheme 1),
this simple photocarbonylation method holds promise as
an alternative to the reported processes based on carbon
monoxide.61,65,66,69 Nevertheless, in order for this to pre-
sent a viable catalytic process, it is essential to promote
product release from the benzoyl complex 5. The addition
of CO gas to the photo-reaction product solution, con-
taining complexes 5 and 6, did result in formation of free
benzaldehyde and the dearomatized carbonyl complex 3.
Moreover, irradiation of a benzene solution of complex 3
under an atmosphere of CO gas allows for catalytic for-
mation of benzaldehyde (Figure S37, ESI). The observed
photocarbonylation of benzene with a pincer rhodium(I)
complex is quite unique, and relies on MLC to trap the C–
H activated species (Scheme 5). Nevertheless, rhodium
catalyzed photocarbonylation of benzene under CO at-
mosphere is known and well-studied.61–66
Pressurizing complex 5 under N2, H2, or CO2 gasses (or
the combination thereof) did not result in significant re-
lease of benzaldehyde. Addition of methanol, ethanol,
phenol, or trifluoroethanol were also attempted for the
release of an acylated product from complex 5, but with
no success. Finally, it was found that strong organic protic
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 12
Most importantly, a clear signal of free benzaldehyde is Scheme 7. Stepwise cycle for carbonylation of ben-
observed in the 1H-NMR spectrum. One new complex can
be assigned to the cationic rhodium carbonyl complex
(4c, Scheme 6), with a TsO- counter ion. This may be a
result of decarbonylation of the benzoyl complexes (ei-
ther 5 or 8), protonated by the added TsOH. The major
product complex, appearing as a doublet in the 31P{1H}-
NMR spectrum at 60 ppm (1JRhP = 147 Hz) with no corre-
sponding hydride, was assigned as (PNP)RhOTs complex
9 (Scheme 6). A third species appears as a doublet in the
31P{1H}-NMR spectrum at 72 ppm (1JRhP = 125 Hz), which is
likely the cationic Rh–N2 complex 10 (with a TsO- counter
ion, Scheme 6), that may form under the nitrogen atmos-
phere. Other minor species with similar spectral features
to complex 9 appear after several hours, however those
could not be identified nor isolated. Thus, oxidative addi-
tion of TsOH to the rhodium(I) benzoyl complex 5 results
in a rhodium(III) hydrido-benzoyl complex (8) which
readily reductively eliminates benzaldehyde and forms
the rhodium(I) complexes 9 and 10. Complex 9 was also
crystallized out of the product mixture and characterized
by X-ray spectroscopy (Figure S50, ESI). Both complexes 9
and 10 could be obtained as a mixture when adding 1
equiv TsOH to a solution of complex 7, in line with their
assignments. The assignment of complex 4c was corrobo-
rated by its independent synthesis from complex 3 and
TsOH. The yield of benzaldehyde from this process was
measured with an internal standard to be 50 % (Figure
S49, ESI). Isolated yield (by vacuum distillation) is lower,
due to the small scale. Yield loss may be explained by the
competing decarbonylation reaction that occurs thermal-
ly under these conditions.61,64,70 Finally, after removing the
volatiles (including the benzaldehyde product), it was
possible to re-form complex 1 (alongside complex 3): Ad-
dition of 1 equiv potassium tert-butoxide base to the
aforementioned complex mixture (9, 10, 4c, and the un-
knowns), followed by filtration in pentane and hydro-
genation under 5.5 bar hydrogen gas, results in a binary
mixture of complexes 1 and 3, that is again viable for the
reductive cleavage of CO2, and subsequent photocar-
bonylation of benzene (Figures S54–S55, ESI).
1
2
3
4
5
6
7
8
zene with CO2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
SUMMARY
Conceptually, a full stepwise cycle for the carbonylation
of benzene using CO2 was achieved. This is not a catalytic
system, since the individual steps in the carbonylation
cycle require variation of the conditions. Nevertheless, it
does illustrate the possibility of combining MLC-based
CO2 splitting with further reactivity of the resulting metal
carbonyl to yield benzaldehyde. The prospect of a PNP
rhodium pincer catalytic system for arene carbonylation
with CO2, potentially replacing the carbon-monoxide
based process, as well as possibly further derivatization of
the produced aldehyde, leading to thermodynamically
viable processes,71 is a highly attractive goal. Tuning of the
physical and chemical conditions of this system is beyond
the scope of this publication, and we are currently striving
to transform this from a stepwise reaction series, into a
catalytic cycle.
EXPERIMENTAL SECTION
General. Rhodium complexes 1, 3, 6, and 7 were synthe-
sized according to previously reported methods.46,59 All
organic reagents were purchased from commercial
sources without further purification. All solvents used
were dried and distilled according to known procedures
to ensure purity and absence of water. CO2 gas, H2 gas,
and CO gas were all purchased from commercial sources
in high pressure cylinders and used without further puri-
fication using Schlenk techniques. 13C labeled CO, and
CO2 gasses were purchased from commercial sources in
lecture bottles and used without further purification us-
ing Schlenk techniques. All reactions were carried out
inside a nitrogen atmosphere glove box or using Schlenk
techniques to ensure oxygen and external water free envi-
ronments. Photoreactions were carried out in a Luzchem
LZC-ORG chamber, equipped with 10 side lamps LZC-
Although a full catalytic cycle for the photocarbonylation
of benzene with CO2 based on complex 1 is not achieved,
it is possible to construct a cycle, in a bottom-up ap-
proach, by sequentially combining the individual stoichi-
ometric steps described above. This has been achieved,
experimetnaly, in miligram scale. The overall process is
summarized schematically in Scheme 7, demonstrating
the current capabilities of the CO2 based photocarbonyla-
tion of benzene with the rhodium(I) PNP pincer com-
plexes.71 This process has been conducted in our lab, with
an overall yield of 30% benzaldehyde isolated, relative to
starting complex 1, in two consecutive cycles (Figures S51–
S56, ESI).
UVB, with peak intensity at 320 nm. H, 13C, and 31P NMR
1
spectra were recorded using Bruker AMX-300, AMX-400,
1
or AMX-500 NMR spectrometers. H and 13C chemical
6
ACS Paragon Plus Environment

Page 7 of 12
Journal of the American Chemical Society
shifts are reported in ppm downfield from tetrame- for X-ray diffraction were grown by slow evaporation of a
1
2
3
4
5
6
7
8
thylsilane and referenced to residual protonated solvent
shifts.72 31P NMR chemical shifts are referenced to an ex-
ternal 85 % solution of phosphoric acid in D2O. All spectra
were recorded at 298 K unless otherwise indicated. Tempera-
ture calibration of the spectrometer was performed using
CH3OH/CD3OD. Abbreviations used in the NMR spectral
assignments: b, broad; s, singlet; d, doublet; dd, doublet
of doublets; t, triplet; q, quartet; m, multiplet; v, virtual.
heptane solution of complex 3, under a dry nitrogen at-
mosphere, at RT. Crystallographic data is given in the ESI
(Table S1).
Reaction of complex 1 with CO2 in water / THF solu-
tion: in-situ formation of [(PNP)RhCO]OH (4a). In a
dry nitrogen glove-box, complex 1 (7.5 mg, 0.015 mmol)
was dissolved in THF (0.4 ml) in an NMR tube sealed with
a septum cap. The tube was taken out of the glove box
and H2O (0.1 ml, deionized and degassed) was added. No
significant changes to the spectral features of complex 1
were observed by NMR. CO2 (336 µL, 1 equiv) was then
injected by a gas tight syringe to the NMR tube, at room
temperature, and the tube was shaken vigorously for 5
min, then an NMR spectrum was recorded, showing full
conversion to the cationic carbonyl complex 4a. Partial
1H-NMR assignments (300 MHz, THF/water, δ): 8.02 (t,
9
Reaction of complex 1 with CO2: in-situ formation of
(PNP)Rh(OCHO) (2). In a dry nitrogen glove box, com-
plex 1 (10.0 mg, 0.02 mmol) was dissolved in toluene-d8
(0.5 ml) in an NMR tube and sealed with a septum cap.
The tube was taken out of the glove box and CO2 (488 µL,
at 1 bar) was injected through the septum cap using a gas-
tight micro syringe. Upon shaking of the tube, the dark
brown solution turned slightly orange within seconds.
Complex 2 could not be isolated, as it gradually converted
thermally in solution to complex 3, or, upon evaporation
of the solution under vacuum, it converted to complex 1.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
3JHH = 7.9 Hz, 1H, Py-H4), 7.71 (d, JHH = 7.9 Hz, 2H, Py-
H3,5), 1.40 – 1.38 (bvt, JPH = 7.2, 7.3 Hz, 36H, PC(CH3)3)
1
ppm; 31P{1H}-NMR (121 MHz, THF/water, δ): 79.5 (d, JRhP
1
NMR Spectroscopic data was taken at 278 K: H-NMR
= 120.3 Hz) ppm. Upon long evaporation of this solution
under high vacuum and dissolution in dry THF, the color
became red again, and a broad signal in the 31P{1H}-NMR
(121 MHz, THF) at 72 – 76 ppm appeared, befitting com-
plex 3. Residual water is observed in the proton spectrum,
accounting for the broad signals.
3
4
(400 MHz, toluene-d8, δ): 8.58 (dt, JRhH = 2.8 Hz, JPH
=
3
1.4 Hz, 1H, RhOCHO), 6.89 (t, JHH = 7.7 Hz, 1H, Py-H4),
3
2
6.25 (d, JHH = 7.6 Hz, 2H, Py-H3,5), 2.52 (t, JPH = 3.4 Hz,
4H, CH2P), 1.40 – 1.34 (bvt, JPH = 6.4, 6.5 Hz, 36H,
PC(CH3)3) ppm; 13C{1H}-NMR (101 MHz, toluene-d8, veri-
fied by HSQC, δ): 168.11 (b, RhOCHO), 164.56 (dvt, JPC
=
Reaction of complex 3 in water / THF solution, in-situ
formation of [(PNP)RhCO]OH (4a). In a dry nitrogen
glove-box, complex 3 (8 mg, 0.015 mmol) was dissolved in
THF (0.4 ml) in an NMR tube sealed with a septum cap.
The tube was taken out of the glove box, H2O (0.2 ml,
deionized and degassed) was added and the tube was
shaken for 5 min. Immediate change of color from red to
yellow-orange was observed. An NMR spectrum was rec-
orded, showing full conversion to the cationic carbonyl
complex 4a. Partial 1H-NMR assignments (300 MHz,
THF/water, δ): 8.00 (b, 1H, Py-H4), 7.71 (b, 2H, Py-H3,5),
1.40 – 1.38 (bvt, JPH = 7.1, 7.3 Hz, 36H, PC(CH3)3) ppm;
2
6.4 Hz, JRhC = 1.2 Hz, Py-C2,6), 129.76 (s, Py-C4) 119.57
(dvt, JPC = 5.1 Hz, 3JRhC = 1.0 Hz, Py-C3,5), 35.69 (dvt, JPC
=
5.5 Hz, 2JRhC = 0.9 Hz, CH2P), 34.47 (dvt, JPC = 5.6 Hz, 2JRhC
= 1.4 Hz, PC(CH3)3), 29.32 (vt, JPC = 3.7 Hz, PC(CH3)3) ppm;
31P{1H}-NMR (162 MHz, toluene-d8, δ): 60.0 (d, 1JRhP = 154.2
Hz) ppm.
Orange crystals of complex 2, suitable for X-ray crystallo-
graphy, were obtained by 5 second bubling of CO2 into a
toluene solution of complex 1 (10 mg complex in 0.5 ml
toluene), followed by addition of pentane (2 ml to the
product tolune solution of complex 2) and keeping at –20
°C for 24 h. Crystallographic data is given in the ESI (Ta-
ble S1).
1
31P{1H}-NMR (121 MHz, THF/water, δ): 79.4 (bd, JRhP = 122
Hz) ppm. These spectral features resemble that of previ-
ously reported [(PNP)RhCO][X] (X
=
BF4, BArf,
Prolonged reaction of complex 1 with CO2 in THF:
formation of (PNP*)RhCO (3). In a dry nitrogen glove
box, complex 1 (10.0 mg, 0.02 mmol) was dissolved in THF
(0.5 ml) in an NMR tube and sealed with a septum cap.
The tube was taken out of the glove box and CO2 (488 µL,
at 1 bar) was injected through the septum cap using a gas-
tight micro syringe. Upon shaking of the tube, the dark
brown solution turned slightly orange within seconds
(formation of complex 2). The tube was then shaken for
5 h at ambient temperature, during which the solution
color gradually turned to red. NMR spectroscopy con-
firmed quantitative conversion to complex 3.
Complex 3 was characterized in a previous publication.46
The UV-Vis absorption spectrum and X-ray crystal struc-
ture are shown in the supporting information (Figures
S29 and S30 respectively). Major UV-Vis absorption bands
(in pentane): 212, 290, 310, 385 nm. Red crystals suitable
OC(O)CF3, Cl).52
Attempted catalytic hydrogenation of CO2 to formate
salt with NEt3. Note: H2 gas is highly explosive and ap-
propriate safety measures should be taken when attempt-
ing these procedures. In a dry nitrogen glove box, com-
plex 1 (17 mg, 0.034 mmol) was charged into a Teflon
lined Parr autoclave, and dissolved in 3 ml THF / NEt3
solution (5 : 1 respectively). The autoclave was taken out
of the box and pressurized first with 20 bar of H2 gas, fol-
lowed by an additional 20 bar CO2 gas. After dissolution
of the gasses, at room temperature, the pressure gauge
registered a total of 36 bar. The solution was stirred at RT
for 20 h. The vessel was then cooled to 0 °C and vented in
a fume hood. The solution was concentrated under vacu-
um. Mesitylene (0.027 mmol) was added as standard and
NMR spectra were recorded in CDCl3. 1H-NMR (300 MHz)
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 12
showed formation of 0.8 mmol formic acid–triethylamine
dissolution in deuterated benzene. Full spectral assign-
31
adduct (TON = 23). P{1H}-NMR (121 MHz) showed a sig-
ment of complex 5 (ca. 75% in the mixture): 1H-NMR (400
MHz, benzene-d6, δ): 8.89 (bd, 3JHH = 6.3 Hz, 1H Benzoyl-
H2,6), 7.42 (m, 2H, Benzoyl-H3,5), 7.22 (m, 1H, Benzoyl-
4), 6.94 (t, 3JHH = 7.6 Hz, 1H, Py-H4), 6.47 (d, 3JHH = 7.6 Hz,
2H, Py-H3,5) 2.93 (vt, JPH = 2.9 Hz, 4H, CH2P), 1.26 (dd
(looks like t), JPH = 6.1, 6.2 Hz, 36H, PC(CH3)3) ppm;
13C{1H}-NMR (100 MHz, benzene-d6, verified by HSQC and
1
2
3
4
5
6
7
8
1
nal at 78.6 (d, JRhP = 121 Hz) ppm, corresponding to com-
plex 4b (vide infra).
Reaction of complex 1 under high pressure CO2 and
H2, formation of [(PNP)RhCO]CHOO (4b). Note: H2
gas is highly explosive and appropriate safety measures
should be taken when attempting these procedures. In a
dry nitrogen glove box, complex 1 (3.5 mg, 7×10-3 mmol)
was charged into a Teflon lined Parr autoclave, and dis-
solved in 3 ml THF. The autoclave was taken out of the
box and pressurized first with 30 bar of H2 gas, followed
by an additional 20 bar CO2 gas. After dissolution of the
gasses, at room temperature, the pressure gauge regis-
tered a total of 42 bar. The solution was stirred at RT for
18 h. The vessel was then cooled to 0 °C and vented in a
fume hood. A sample (0.5 ml) was taken of the product
1
2
HMBC, δ): 264.7 (dt, JRhC = 34.5 Hz, JPC = 8.6 Hz,
RhC(O)Ph), 132.7 (Benzoyl-C2,6), 127.1 (Benzoyl-C3,5),
119.3 (Benzoyl-C4), 37.8 (vt, JPC = 5.0 Hz, CH2P), 35.5 (bm,
PC(CH3)3), 30.0 (b, PC(CH3)3) ppm; 31P{1H}-NMR (121.5
MHz, benzene-d6, δ): 59.90 (d, 1JRhP = 187.4 Hz) ppm.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Independent synthesis of (PNP)RhCOPh (5). In a dry
nitrogen glove box, complex 7 (20 mg, 0.038 mmol) and
benzaldehyde (4.8 mg, 1.2 equiv) were dissolved in ben-
zene (1.5 ml) inside a Schlenk tube. The solution was fro-
zen in liquid nitrogen and vacuum was applied for 30 sec,
to reduce the partial pressure of nitrogen gas. The solu-
tion was stirred for 12 h under reduced pressure, at ambi-
ent temperature. The red solution turned greenish-
1
solution and a H-NMR spectrum was recorded, showing
formation of complex 4b and a signal befitting a formate
moiety. An 8 : 1 ratio of the formate signal (8.1 ppm) ver-
sus the product complex signal (complex 4b, signal at
7.97 ppm, t, Py-H4) was observed. The solution was evap-
orated under high vacuum and the residue dissolved in
acetone-d6 for NMR spectroscopy. Residual formic acid,
and deuterium exchange affect the spectral features. Nev-
ertheless, it is in line with previously reported cationic
[(PNP)RhCO]+ fragments.52 1H-NMR (400 MHz, acetone-
d6, δ): 8.59 (b, 1H (overlapping with excess residual formic
acid), HCOO), 8.04 (t, 3JHH = 7.8 Hz, 1H, Py-H4), 7.74 (3JHH
= 7.8 Hz, 2H, Py-H3,5), 4.18 (bm, 4H (2.8H by integration
due to deuterium exchange), CH2P), 1.46 (m, 36H,
PC(CH3)3) ppm; 13C{1H}-NMR (partial assignment, from
HSQC, 400 MHz, acetone-d6, δ): 165.6 (HCOO), 138.0 (Py-
1
brown, with >95% formation (by H-NMR) of complex 5,
with identical spectroscopic assignment to that formed by
photocarbonylation (above). Crystals suitable for X-ray
diffraction were grown by the dissolution of complex 5 in
minimum pentane containing benzaldehyde (1 equiv ex-
cess), keeping at -20°C for a week. Crystallographic data is
given in the ESI (Table S1).
Reaction of complex 5 with TsOH, in-situ formation
of (PNP)Rh(H)(OTs)COPh (8), (PNP)RhOTs (9), and
free benzaldehyde. In a dry nitrogen glove box, complex
5 (15 mg, 0.025 mmol) was charged in an NMR tube and
dissolved in toluene-d8 (0.5 ml). The solution was cooled
to -20°C by placing the tube in the freezer. Then, 1,4-
dioxane (1 equiv, 2.2 mg) and TsOH (1 equiv, 4.3 mg) were
added to the NMR tube, and it was taken out of the glove
box and put in the pre-cooled NMR spectrometer at 275
K. Spectra were recorded at various temperatures, howev-
er coherent spectral data could only be obtained at 290 K.
Due to overlapping of the various products, only partial
assignment could be achieved of complex 8 (aromatic
region signals overlapping solvent and benzaldehyde): 1H-
C4), 122.4 (Py-C3,5), 36.4 (CH2P), 29.5 (PC(CH3)3) ppm;
1
31P{1H}-NMR (162 MHz, acetone-d6, δ): 79.48 (d, JRhP
=
120.6 Hz (fine deuterium coupling due to deuterium ex-
change on the ligand backbone, features a doublet of
multiplet with JDP = 17 Hz).
Photocarbonylation of benzene by complex 3, in-situ
formation of (PNP)RhCOPh (5). In a dry nitrogen glove
box, complex 3 (10 mg, 0.019 mmol) was dissolved in ben-
zene (0.5 ml). The tube was irradiated under UV(B), at
ambient temperature, for 72 h. With irradiation, the solu-
tion color gradually turned from bright red to brown. The
3
NMR (500 MHz, toluene-d8, δ): 8.22 (d, JHH = 6.1 Hz, 2H,
3
TsO(H2,6)), 8.11 (d, JHH = 5.4 Hz, 2H, COPh(H2,6)), 7.73
1
reaction was monitored by H and 31P NMR, showing for-
(t, 3JHH = 7.6 Hz, 1H, Py-H4), 7.66 (d, 3JHH = 7.6 Hz, 2H, Py-
H3,5), 4.51, 3.59 (ABq, JAB = 17.0 Hz, 4H, CH2P) 2.14 (s, 1H,
mation of complexes 3 / 6 / 5 in 1 : 3 : 16 ratios, respective-
1
ly. In-situ spectroscopic indication of complex 5: H-NMR
OTs(CH3)), 1.18 (bvt, JPH = 6.7, 6.8 Hz, 18H, PC(CH3)3), 1.06
3
1
(300 MHz, benzene, δ): 8.86 (bd, JHH = 6.3 Hz, Benzoyl-
(bvt, JPH = 6.3, 6.4 Hz, 18H, PC(CH3)3), -19.13 (dt, JRhH
=
H2,6), 2.93 (b, CH2P), 1.25 (bm, PC(CH3)3) ppm; 31P{1H}-
29.6 Hz, JPH = 11.7 Hz, 1H, Rh–H) ppm; 31P{1H}-NMR (202
2
1
1
NMR (121.5 MHz, benzene, δ): 59.90 (d, JRhP = 187.4 Hz)
MHz, toluene-d8, δ): 64.6 (bd, JRhP = 114.61 Hz) ppm;
ppm. The formation of benzoyl complex 5 was also con-
firmed in-situ by 13C NMR, when starting from the 13C la-
beled carbonyl complex 3 in the same experimental pro-
cedure: 13C{1H}-NMR (75 MHz, benzene, δ): 264.7 (dt, 1JRhC
= 34.5 Hz, 2JPC = 8.6 Hz, RhCOPh) ppm. Full characteriza-
tion of complex 5 (in mixture with complexes 3 and 6)
was possible after evaporation of the reaction solvent and
13C{1H}-NMR (125 MHz, toluene-d8, correlated by HSQC,
δ): 37.1 (b, CH2P), 21.3 (OTs(CH3)), 29.5 (PC(CH3)3) ppm.
At room temperature, within an hour, complexes 4c, 9,
and 10 appear and are identifiable by 31P{1H}-NMR (202
MHz, toluene-d8, δ): 79.4 (d, 1JRhP = 120.2 Hz, complex 4c),
1
1
71.5 (d, JRhP = 125.3 Hz, complex 10), 60.3 (d, JRhP = 147.3
Hz, complex 9) ppm. Two other species form, which
8
ACS Paragon Plus Environment

Page 9 of 12
Journal of the American Chemical Society
could not be unequivocally identified, and may be iso-
7.9 Hz, 2H TsO-(H3,5)), 4.24 (bvt, JPH = 3.6, 3.7 Hz 4H,
CH2P), 2.10 (s, 3H, OTs(CH3)), 1.15 (bvt, JPH = 15.6, 8.4 Hz,
36H, PC(CH3)3) ppm; 13C{1H}-NMR (125 MHz, benzene-d6,
δ): 196.24 (b, Rh-CO), 165.76 (vt, JPC = 5.7 Hz, Py-C2,6),
147.25 (TsO-C4(ipso)), 141.05 (Py-C4), 138.02 (TsO-
C1(CipsoSO)), 128.57 (TsO-(C3,5), 127.18 (TsO-(C3,5C2,6)),
123.72 (vt, JPC = 4.7 Hz, Py-C3,5), 36.25 (vt, JPC = 9.6 Hz,
CH2P), 35.71 (vt, JPC = 9.2, PC(CH3)3), 29.24 (vt, JPC = 2.8
Hz, PC(CH3)3), 21.23 (OTs-CH3) ppm; 31P{1H}-NMR (121
31
mers of the identified complexes: P{1H}-NMR (202 MHz,
1
2
3
4
5
6
7
8
toluene-d8, δ): 63.4 (d, 1JRhP = 116.6 Hz, unknown), and 62.5
1
(d, JRhP = 145.4 Hz, unknown) ppm. Brown crystals of
complex 9, suitable for X-ray crystallography, were collec-
ted from the toluene product mixture that was kept at -20
°C for a week. The crystal structure of complex 9 is depicted
in Figure S50 in the ESI. Crystallographic data is given in
the ESI (Table S1).
1
9
MHz, C6D6, δ): 79.62 (d, JRhP = 120.0 Hz). IR: νCO = 1971
Reaction of complex 7 and TsOH, formation of
[(PNP)RhN2]TsO (10) and (PNP)RhOTs (9). In a dry
nitrogen glove box, complex 7 (6.1 mg, 0.01 mmol) and
TsOH (2.0 mg, 1 equiv) were dissolved in C6D6 (0.5 ml).
NMR spectroscopy revealed the formation of complexes 9
and 10 in a 1 : 9 ratio. Complex 10 is similar to previously
reported [(PNP)RhN2]+ fragments,59 and was character-
cm-1.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Sequential photocarbonylation cycles of benzene
with CO2. In a dry nitrogen glove box, complex 1 (20.0
mg, 0.04 mmol) was dissolved in THF (0.5ml) inside a J.
Young NMR tube. The solution was frozen in liquid nitro-
gen and vacuum was pumped for 1 minute, then let thaw,
and opened to a 1 bar CO2 atmosphere, sealed and shaken
vigorously for 5 min. NMR spectroscopy showed for-
mation of complex 2. The solution was shaken in the
closed tube for 5 h, until NMR spectroscopy showed over
90% conversion to complex 3. The solution was then
evaporated under high vacuum to dryness, and re-
dissolved in benzene (1.5 ml) to fill the entire NMR tube
volume. The benzene filled tube was introduced to the
irradiation chamber and irradiated under UV(B) for 72 h.
NMR spectroscopy showed formation of complexes 5 and
6 in a 5 : 1 ratio, respectively, with less than 5 % unreacted
complex 3. The solution was then transferred into a
Schlenk flask in the dry nitrogen glove box. TsOH (7.0
mg, 1 equiv to complex 1) was added and the solution was
stirred for 24 h, during which the color changed from
brown to yellow to dark red. The Schlenk flask was then
connected to a receiver flask, and using freeze-pump
technique all volatiles were distilled out and collected in
the receiver flask. To the distillate solution was added
mesitylene (5.6 mg, 0.046 mmol) as an internal standard
and the amount of benzaldehyde thus produced was
1
ized by H and 31P NMR spectroscopy. The solution was
then heated to 65 °C for 1 h, and complex 9 was formed in
1
a 13 : 1 ratio to complex 10. Complex 9: H-NMR (400
3
MHz, benzene-d6, δ): 8.10 (d, JHH
= 8.1 Hz, 2H,
OTs(H2,5)), 6.91 (d, 3JHH = 7.9 Hz, 2H, OTs(H3,5)), 6.86 (t,
3
3JHH = 7.6 Hz, 1H, Py-H4)), 6.26 (d, JHH = 7.6 Hz, 2H, Py-
H2,3)), 2.54 (vt, JPH = 3.3 Hz, 4H, CH2P), 2.00 (s, 3H,
OTs(CH3)), 1.47 – 1.38 (bvt, JPH = 6.5, 6.6 Hz, 36H,
PC(CH3)3) ppm; 13C{1H}-NMR (101 MHz, benzene-d6, δ):
165.90 (vt, JPC = 5.7 Hz, Py-C2,6), 144.53 (TsO-C4(ipso)),
138.67 (TsO-C1(CipsoSO)), 130.63 (Py-C4), 128.47 (OTs-
C3,5), 127.13 (OTs-C2,6), 119.60 (vt, JPC = 4.7 Hz, Py-C3,5),
36.13 (vt, JPC = 5.6 Hz, CH2P), 34.49 (vt, JPC = 5.9, 6.5,
PC(CH3)3), 29.38 (vt, JPC = 3.5 Hz, PC(CH3)3), 21.16 (OTs-
CH3) ppm; 31P{1H}-NMR (162 MHz, benzene-d6, δ): 60.17
(d, 1JRhP = 147.6 Hz) ppm. Complex 10: 1H-NMR (300 MHz,
3
C6D6, δ): 8.43 (overlapping doublets, JHH = 6.0, 6.4 Hz,
4H, TsO-), 7.42 (t, 3JHH = 7.8 Hz, 1H, Py-H4), 7.05 (d, 3JHH
=
7.9 Hz, 2H, Py-H3,5), 4.06 (vt, JPH = 3.9 Hz, 4H, CH2P),
-
2.10 (s, 3H, OTs(CH3)), 1.19 (bvt, JPH = 13.9, 6.8 Hz, 36H,
PC(CH3)3) ppm; 31P{1H}-NMR (121 MHz, C6D6, δ): 71.72 (d,
1JRhP = 124.8 Hz). Another unidentified complex was
formed with 31P{1H}-NMR (121 MHz, benzene-d6, δ): 62.5
1
measured by H-NMR (7.2×10-3 mmol, 18% overall yield
relative to complex 1). In a dry nitrogen glove box, to the
dry organometallic residues from the reaction flask was
added THF (1.5 ml) and potassium tert-butoxide (4.8 mg,
0.04 mmol). The solution was stirred for 3 h, and then
evaporated under high vacuum. The solids were extracted
to pentane (2 ml), filtered through Celite, and evaporated
to dryness (20.2 mg red solid obtained). NMR spectrosco-
py of the product showed formation of complexes 7 and 3
in a 3 : 1 ratio. This mixture was dissolved in pentane in a
Fischer Porter pressure vessel, pressed with 5.5 bar H2 gas,
and stirred for 2 days at room temperature. Note: H2 gas
is highly explosive and appropriate safety measures
should be taken when attempting these procedures. After
evaporation of the volatiles, 18.9 mg brown powder was
obtained of complex 1 in a 3 : 1 mixture with complex 3 (93
% Rh recovery). This mixture was dissolved in THF (0.5
ml) in a J. young NMR tube and the whole procedure was
repeated as described above, producing additional 4.7×10-3
mmol benzaldehyde (12 % additional yield, relative to
1
(d, JRhP = 145.5 Hz) ppm. This is possibly an isomer of
complex 9, and appears in the reactions of TsOH with
complex 5 (vide supra) but this could not be asserted, as
its spectral features overlap with those of complex 9.
Reaction of complex 3 with TsOH, independent syn-
thesis of [(PNP)RhCO]TsO (4c). In a dry nitrogen glove
box, complex 3 (6.5 mg, 0.012 mmol) and TsOH (2.2 mg,
1.05 equiv) were mixed in C6D6 (0.5 ml) in an NMR tube.
The mixture was shaken vigorously for 15 min until the
solution color turned from red to yellow, with the for-
mation of the cationic complex 4c. The carbonyl IR
stretch is at lower frequency than the previously reported
[(PNP)RhCO][X] (X = BF4, BArf, OC(O)CF3, Cl),52 suggest-
ing partial coordination of the TsO- moiety. Reasonable
solubility of the complex in benzene would suggest this as
1
3
well. H-NMR (300 MHz, benzene-d6, δ): 8.53 (bd, JHH
=
7.0 Hz, 2H, Py-H3,5), 8.39 (d, JHH = 7.9 Hz, 2H, TsO-
(H2,6)), 7.60 (t, JHH = 7.0 Hz, 1H, Py-H4), 7.04 (d, JHH
3
3
3
=
9
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 12
Int. Ed. 2015, 54, 10220–10224. (f) Zhang, Z.; Liao, L.-L.;
original amount of complex 1). Overall yield of benzalde-
hyde in two cycles (based on starting amount of complex
1) is 30%.
1
2
3
Yan, S.-S.; Wang, L.; He, Y.-Q.; Ye, J.-H.; Li, J.; Zhi, Y.-
G.; Yu, D.-G. Angew. Chem., Int. Ed. 2016, 55, 7068–
7072.
(6) Reviews: (a) Behr, A. Chem. Ing. Tech. 1985, 57, 893–
903. (b) Walther, D. Coord. Chem. Rev. 1987, 79, 135–
174. (c) Leitner, W. Angew. Chem., Int. Ed. Engl. 1995,
34, 2207–2221. (d) Cokoja, M.; Bruckmeier, C.; Rieger,
B.; Herrmann, W. A.; Kühn, F. E. Angew. Chem., Int.
Ed. 2011, 50, 8510–8537. (e) Huang, K.; Sun, C.-L. ; Shi,
Z.-J. Chem. Soc. Rev. 2011, 40, 2435–2452. (f) Wu, L.;
Liu, Q.; Jackstell, R.; Beller, M. Angew. Chem., Int. Ed.
2014, 53, 6310–6320. (g) Liu, Q.; Wu, L.; Jackstell, R.;
Beller, M. Nat. Commun. 2015, 6, 5933.
(7) Arakawa, H.; Aresta, M.; Armor, J. N.; Barteau, M. A.;
Beckman, E. J.; Bell, A. T.; Bercaw, J. E.; Creutz, C.;
Dinjus, E.; Dixon, D. A.; Domen, K.; DuBois, D. L.;
Eckert, J.; Fujita, E.; Gibson, D. H.; Goddard, W. A.;
Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H. H.;
Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.;
Nicholas, K. M.; Periana, R.; Que, L.; Rostrup-Nielson,
J.; Sachtler, W. M. H.; Schmidt, L. D.; Sen, A.; Somorjai,
G. A.; Stair, P. C.; Stults, B. R.; Tumas, W. Chem. Rev.
2001, 101, 953–996.
(8) Hossain, S. F.; Nicholas, K. M.; Teas, C. L.; Davis, R. E.
J. Chem. Soc., Chem. Commun. 1981, 268–269.
(9) Lin, W.; Han, H.; Frei, H. J. Phys. Chem. B 2004, 108,
18269–18273.
(10) Goettmann, F.; Thomas, A.; Antonietti, M. Angew.
Chem., Int. Ed. 2007, 46, 2717–2720.
(11) Gu, L.; Zhang, Y. J. Am. Chem. Soc. 2010, 132, 914–915.
(12) Ménard, G.; Stephan, D. W. Angew. Chem., Int. Ed.
2011, 50, 8396–8399.
(13) Palit, C. M.; Graham, D. J.; Chen, C.-H.; Foxman, B. M.;
Ozerov, O. V. Chem. Commun. 2014, 50, 12840–12842.
(14) Das Neves Gomes, C.; Blondiaux, E.; Thuéry, P.; Can-
tat, T. Chem.—Eur. J. 2014, 20, 7098–7106.
4
5
6
7
8
9
ASSOCIATED CONTENT
NMR spectra for new complexes, additional experimental
details and spectral data. this material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Corresponding Author
* E-mail for D.M.: david.milstein@weizmann.ac.il.
Author Contributions
All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This research was supported by the Israel Science Founda-
tion, the ASER (Alternative Sustainable Energy Research)
fund, and by the Helen and Martin Center for Molecular
Design. D.M. holds the Israel Matz Professorial Chair of Or-
ganic Chemistry.
ABBREVIATIONS
THF, tetrahydrofuran; UV, ultraviolet; NMR, nuclear mag-
netic resonance; IR, infrared; GC, gas chromatography.
REFERENCES
(1) (a) Harlow, R. L.; Kinney, J. B.; Herskovitz, T. J. Chem.
Soc., Chem. Commun. 1980, 813–814. (b) Tominaga, K.-
I.; Sasaki, Y. Catal. Commun. 2000, 1, 1–3. (c) Tomina-
ga, K.-I.; Sasaki, Y. J. Mol. Catal A: Chem. 2004, 220,
159–165.
(2) (a) Fischer, R.; Langer, J.; Malassa, A.; Walther, D.;
Görls, H.; Vaughan, G. Chem. Commun. 2006, 2510–
2512. (b) Silvia, J. S.; Cummins, C. C. J. Am. Chem. Soc.
2010, 132, 2169–2171. (c) Mizuno, H.; Takaya, J.; Iwa-
sawa, N. J. Am. Chem. Soc. 2011, 133, 1251–1253. (d) Uhe,
A.; Hölscher, M.; Leitner, W. Chem.—Eur. J. 2012, 18,
170–177.
(3) Ostapowicz, T. G.; Schmitz, M.; Krystof, M.; Klanker-
mayer, J.; Leitner, W. Angew. Chem., Int. Ed. 2013, 52,
12119–12123.
(4) Liu, Q.; Wu, L.; Fleischer, I.; Selent, D.; Franke, R.;
Jackstell, R.; Beller, M. Chem.—Eur. J. 2014, 20, 6888–
6894.
(5) (a) Tani, Y.; Kuga, K.; Fujihara, T.; Terao, J.; Tsuji, Y.
Chem. Commun. 2015, 51, 13020–13023. (b) Xin, Z.; Les-
cot, C.; Friis, S. D.; Daasbjerg, K.; Skrydstrup, T. Angew.
Chem., Int. Ed. 2015, 54, 6862–6866. (c) Stieber, S. C.
E.; Huguet, N.; Kageyama, T.; Jevtovikj, I.; Ariyananda,
P.; Gordillo, A.; Schunk, S. A.; Rominger, F.; Hofmann,
P.; Limbach, M. Chem. Commun. 2015, 51, 10907–10909.
(d) Masuda, Y.; Ishida, N.; Murakami, M. J. Am. Chem.
Soc. 2015, 137, 14063–14066. (e) Keane, A. J.; Farrell, W.
S.; Yonke, B. L.; Zavalij, P. Y.; Sita, L. R. Angew. Chem.,
(15) Zhang, M.; El-Roz, M.; Frei, H.; Mendoza-Cortes, J. L.;
Head-Gordon, M.; Lacy, D. C.; Peters, J. C. J. Phys.
Chem. C 2015, 119, 4645–4654.
(16) Allen, O. R.; Dalgarno, S. J.; Field, L. D. Organometal-
lics 2008, 27, 3328–3330.
(17) Sampson, M. D.; Kubiak, C. P. J. Am. Chem. Soc. 2016,
138, 1386–1393.
(18) Reviews: (a) Centi, G.; Perathoner, S. Catal. Today
2009, 148, 191–205. (b) Wang, W.; Wang, S.; Ma, X.;
Gong, J. Chem. Soc. Rev. 2011, 40, 3703–3727.
(19) Scheuermann, M. L.; Semproni, S. P.; Pappas, I.; Chirik,
P. J. Inorg. Chem. 2014, 53, 9463–9465.
(20) Riplinger, C.; Sampson, M. D.; Ritzmann, A. M.; Kubi-
ak, C. P.; Carter, E. A. J. Am. Chem. Soc. 2014, 136,
16285–16298.
(21) Reviews: (a) Tanaka, K. Bull. Chem. Soc. Jpn. 1998, 71,
17–29. (b) Jessop, P. G.; Ikariya, T.; Noyori, R. Chem.
Rev. 1995, 95, 259–272. (c) Fukuzumi, S.
Eur. J.
Inorg. Chem. 2008, 2008, 1351–1362. (d) Alberico, E.;
Nielsen, M. Chem. Commun. 2015, 51, 6714–6725.
(22) (a) Bo, C.; Didieu, A. Inorg. Chem. 1989, 28, 304–309.
(b) Hou, C. ; Jiang, J. ; Zhang, S. ; Wang, G. ; Zhang, Z.;
Ke, Z.; Zhao, C. ACS Catal. 2014, 4, 2990–2997. (c)
Mondal, B.; Neese, F.; Ye, S. Inorg. Chem. 2015, 54,
7192– 7198. (d) Ni, S.-F.; Dang, L. Phys. Chem. Chem.
Phys. 2016, 18, 4860–4870.
10
ACS Paragon Plus Environment

Page 11 of 12
Journal of the American Chemical Society
(23) (a) Jessop, P. G.; Joó, F.; Tai, C. Coord. Chem. Rev. 2004,
(36) (a) Rezayee, N. M.; Huff, C. A.; Sanford, M. S. J. Am.
Chem. Soc. 2015, 137, 1028-1031. (b) Khusnutdinova, J.
R.; Garg, J. A.; Milstein, D. ACS Catal. 2015, 5, 2416–
2422. (c) Kothandaraman, J.; Goeppert, A.; Czaun, M.;
Olah, G. A.; Prakash, G. K. S. J. Am. Chem. Soc. 2016,
138, 778–781.
(37) (a) Zhang, L.; Han, Z.; Zhao, X.; Wang, Z.; Ding, K. An-
gew. Chem., Int. Ed. 2015, 54, 6186–6189. (b) Kang, B.;
Hong, S. H. Adv. Synth. Catal. 2015, 357, 834–840.
(38) (a) Hutschka, F.; Dedieu, A.; Leitner, W. Angew.
Chem., Int. Ed. Eng. 1995, 34, 1742–1745. (b) Huang, K.-
W.; Han, J. H.; Musgrave, C. B.; Fujita, E. Organometal-
lics 2007, 26, 508–513. (c)Vigalok, A.; Ben-David, Y.;
Milstein, D. Organometallics 1996, 15, 1839–1844. (d)
Musashi, Y.; Sakaki, S. J. Chem. Soc., Dalton Trans.
1998, 577–584. (e) Pomelli, C. S.; Tomasi, J.; Solá, M.
Organometallics 1998, 17, 3164–3168. (f) Yoshida, T.;
Thorn, D. L.; Okanko, T.; Ibers, J. A.; Otsuka, S. J. Am.
Chem. Soc. 1979, 101, 4212–4221.
1
2
3
4
5
6
7
8
248, 2425–2442. (b) Creutz, C.; Chou, M. H. J. Am.
Chem. Soc. 2007, 129, 10108–10109. (c) Schmeier, T. J.;
Hazari, N.; Incarvito, C. D.; Raskatov, J. A. Chem.
Commun. 2011, 47, 1824–1826. (d) Schmeier, T. J.;
Dobereiner, G. E.; Crabtree, R. H.; Hazari, N. J. Am.
Chem. Soc. 2011, 133, 9274–9277.
(24) (a) Tsai, J. C.; Nicholas, K. M. J. Am. Chem. Soc. 1992,
114, 5117–5124. (b) Graf, E.; Leitner, W. J. Chem. Soc.,
Chem. Commun. 1992, 623–624. (c) Leitner, W.; Dinjus,
E.; Gaßner, F. J. Organomet. Chem. 1994, 475, 257–266.
(25) (a) Jessop, P. G.; Ikariya, T.; Noyori, R. Nature 1994,
368, 231–233. (b) Fornika, R.; Görls, H.; Seemann, B.;
Leitner, W. J. Chem. Soc., Chem. Commun. 1995, 1479–
1481. (c) Jessop, P. G.; Hsiao, Y.; Ikariya, T.; Noyori, R. J.
Am. Chem. Soc. 1996, 118, 344–355. (d) Joó, F.; Lau-
renczy, G.; Nádasdi, L.; Elek, J. Chem. Commun. 1999,
971–972. (e) Tai, C.-C.; Pitts, J.; Linehan, J. C.; Main, A.
D.; Munshi, P.; Jessop, P. G. Inorg. Chem. 2002, 41,
1606–1614. (f) Munshi, P.; Main, A. D.; Linehan, J. C.;
Tai, C.-.C; Jessop, P. G. J. Am. Chem. Soc. 2002, 124,
7963–7971. (g) Ng, S. M.; Yin, C.; Yeung, C. H.; Chan, T.
C.; Lau, C. P. Eur. J. Inorg. Chem. 2004, 2004, 1788–
1793. (h) Hayashi, H.; Ogo, S.; Fukuzumi, S. Chem.
Commun. 2004, 2714–2715.
(26) (a) Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem.
Soc. 2009, 131, 14168–14169. (b) Federsel, C.; Boddien,
A.; Jackstell, R.; Jennerjahn, R.; Dyson, P. J.; Scopelliti,
R.; Laurenczy, G.; Beller, M. Angew. Chem., Int. Ed.
2010, 49, 9777–9780. (c) Hull, J. F.; Himeda, Y.; Wang,
W.-H.; Hashiguchi, B.; Periana, R.; Szalda, D. J.; Muck-
erman, J. T.; Fujita, E. Nat. Chem. 2012, 4, 383–388.
(27) Langer, R.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J.
W.; Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed.
2011, 50, 9948–9952.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(39) Musashi, Y.; Sakaki, S. J. Am. Chem. Soc. 2002, 124,
7588–7603.
(40) Reviews: (a) Khusnutdinova, J. R.; Milstein, D. Angew.
Chem., Int. Ed. 2015, 54, 12236–12273. (b) Gunanathan,
C.; Milstein, D. Bond Activation by Metal-Ligand Co-
operation: Design of “Green” Catalytic Reactions Based
on Aromatization-Dearomatization of Pincer Com-
plexes. In Ikariya, T., Shibasaki, M., Eds.; Springer Ber-
lin Heidelberg: 2011; Vol. 37, pp 55–84. (c) Zell, T.; Mil-
stein, D. Acc. Chem. Res. 2015, 48, 1979–1994. (d) Gun-
anathan, C.; Milstein, D. Acc. Chem. Res. 2011, 44, 588–
602.
(41) (a) Montag, M.; Zhang, J.; Milstein, D. J. Am. Chem.
Soc. 2012, 134, 10325–10328. (b) Zhang, J.; Leitus, G.;
Ben-David, Y.; Milstein, D. J. Am. Chem. Soc. 2005, 127,
10840–10841. (c) Gunanathan, C.; Ben-David, Y.; Mil-
stein, D. Science 2007, 317, 790–792. (d) Fogler, E.;
Garg, J. A.; Hu, P.; Leitus, G.; Shimon, L. J. W.; Mil-
stein, D. Chem.—Eur. J. 2014, 20, 15727–15731. (e) Hu,
P.; Diskin-Posner, Y.; Ben-David, Y.; Milstein, D. ACS
Catal. 2014, 4, 2649–2652.
(42) (a) Gunanathan, C.; Gnanaprakasam, B.; Iron, M. A.;
Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2010,
132, 14763–14765. (b) Balaraman, E.; Gnanaprakasam,
B.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc.
2010, 132, 16756–16758. (c) Feller, M.; Diskin-Posner, Y.;
Shimon, L. J. W.; Ben-Ari, E.; Milstein, D. Organome-
tallics 2012, 31, 4083–4101.
(43) (a) Vogt, M.; Nerush, A.; Iron, M. A.; Leitus, G.; Diskin-
Posner, Y.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D.
J. Am. Chem. Soc. 2013, 135, 17004–17018. (b) Nerush, A.;
Vogt, M.; Gellrich, U.; Leitus, G.; Ben-David, Y.; Mil-
stein, D. J. am. Chem. Soc. 2016, 138, 6985–6997.
(44) Anaby, A.; Butschke, B.; Ben-David, Y.; Shimon, L. J.
W.; Leitus, G.; Feller, M.; Milstein, D. Organometallics
2014, 33, 3716–3726.
(28) Kang, P.; Cheng, C.; Chen, Z.; Schauer, C. K.; Meyer, T.
J.; Brookhart, M. J. Am. Chem. Soc. 2012, 134, 5500–
5503.
(29) (a) Filonenko, G. A.; Conley, M. P.; Copéret, C.; Lutz,
M.; Hensen, E. J. M.; Pidko, E. A. ACS Catal. 2013, 3,
2522–2526. (b) Moret, S.; Dyson, P. J.; Laurenczy, G.
Nat. Commun. 2014, 5, 4017. (c) Nakada, A.; Koike, K.;
Nakashima, T.; Morimoto, T.; Ishitani, O. Inorg. Chem.
2015, 54, 1800–1807. (d) Watari, R.; Kayaki, Y.; Hirano,
S.-I.; Matsumoto, N.; Ikariya, T. Adv. Synth. Catal 2015,
357, 1369–1373. (e) Chakraborty, S.; Blacque, O.; Berke,
H. Dalton Trans. 2015, 44, 6560–6570.
(30) Lilio, A. M.; Reineke, M. H.; Moore, C. E.; Rheingold,
A. L.; Takase, M. K.; Kubiak, C. P. J. Am. Chem. Soc.
2015, 137, 8251–8260.
(31) Zhang, Y.; Williard, P. G.; Bernskoetter, W. H. Organ-
ometallics 2016, 35, 860–865.
(32) Reviews: (a) Wang, W.-H.; Himeda, Y.; Muckerman, J.
T.; Manbeck, G. F.; Fujita, E. Chem. Rev. 2015, 115, 2936–
12973. (b) Mellmann, D.; Sponholz, P.; Jungea, H.; Bel-
ler, M. Chem. Soc. Rev. 2016 [Advance article]. doi:
10.1039/C5CS00618J. Published Online: April 27, 2016.
(33) Zell, T.; Butschke, B.; Ben-David, Y.; Milstein, D.
Chem.—Eur. J. 2013, 19, 8068–8072.
(34) Jongbloed, L. S.; de Bruin, B.; Reek, J. N. H.; Lutz, M.;
van der Vlugt, J. I. Catal. Sci. Technol. 2016, 6, 1320–
1327.
(45) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew.
Chem., Int. Ed. 2006, 45, 1113–1115.
(46) Schwartsburd, L.; Iron, M. A.; Konstantinovski, L.; Ben-
Ari, E.; Milstein, D. Organometallics 2011, 30, 2721–
2729.
(47) Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D. An-
gew. Chem., Int. Ed. 2011, 50, 2120–2124.
(35) Federsel, C.; Jackstell, R.; Beller, M. Angew. Chem., Int.
Ed. 2010, 49, 6254–6257.
11
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 12
(48) Feller, M.; Ben-Ari, E.; Diskin-Posner, Y.; Carmieli, R.;
(61) Rosini, G. P.; Boese, W. T.; Goldman, A. S. J. Am. Chem.
1
2
3
4
5
6
7
8
Weiner, L.; Milstein, D. J. Am. Chem. Soc. 2015, 137,
4634–4637.
Soc. 1994, 116, 9498–9505.
(62) (a) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984,
106, 1650–1663. (b) Ghosh, C.K.; Graham, W. A. G. J.
Am. Chem. Soc. 1987, 109, 4726–4727. (c) Spillett, C.;
Ford, P. C. J. Am. Chem. Soc. 1989, 111, 1932–1933.
(63) Boyd, S. E.; Field, L. D.; Partridge, M. G. J. Am. Chem.
Soc. 1994, 116, 9492–9497.
(64) (a) Kunin, A. J.; Eisenberg, R. Organometallics 1988, 7,
2124–2129. (b) Kunin, A. J.; Eisenberg, R. J. Am. Chem.
Soc. 1986, 108, 535–536. (c) Fisher, B. J.; Eisenberg, R.
Organometallics 1983, 2, 764–767.
(49) Gunanathan, C.; Milstein, D. Science 2013, 341, 1229712.
(50) (a) Vogt, M.; Rivada-Wheelaghan, O.; Iron, M. A.; Lei-
tus, G.; Diskin-Posner, Y.; Shimon, L. J.,W.; Ben-David,
Y.; Milstein, D. Organometallics , 32, 300–308. (b) Vogt,
M.; Gargir, M.; Iron, M. A.; Diskin-Posner, Y.; Ben-
David, Y.; Milstein, D. Chem.—Eur. J. 2012, 18, 9194–
9197.
(51) Feller, M.; Gellrich, U.; Anaby, A.; Diskin-Posner, Y.;
Milstein, D. J. Am. Chem. Soc. 2016, 138, 6445–6454.
(52) Feller, M.; Ben-Ari, E.; Gupta, T.; Shimon, L. J. W.; Lei-
tus, G.; Diskin-Posner, Y.; Weiner, L.; Milstein, D. In-
org. Chem. 2007, 46, 10479–10490.
(53) Feller, M.; Ben-Ari, E.; Iron, M. A.; Diskin-Posner, Y.;
Leitus, G.; Shimon, L. J. W.; Konstantinovski, L.; Mil-
stein, D. Inorg. Chem. 2010, 49, 1615–1625.
(54) Iron, M. A.; Ben-Ari, E.; Cohen, R.; Milstein, D. Dalton
Trans. 2009, 9433–9439.
(55) Bennett, M. A. J. Mol. Catal. 1987, 41, 1–20.
(56) (a) Sakaki, S.; Musashi, Y. Int. J. Quantum Chem. 1996,
57, 481–491. (b) Musashi, Y.; Sakaki, S. J. Am. Chem.
Soc. 2000, 122, 3867–3877. (c) Ohnishi, Y.; Matsunaga,
T.; Nakao, Y.; Sato, H.; Sakaki, S. J. Am. Chem. Soc.
2005, 127, 4021–4032. (d) Pu, L. S.; Yamamoto, A.;
Ikeda, S. J. Am. Chem. Soc. 1968, 90, 3896–3896.
(57) Calabrese, J. C.; Herskovitz, T.; Kinney, J. B. J. Am.
Chem. Soc. 1983, 105, 5914–5915.
(58) (a) Grushin, V. V.; Kuznetsov, V. F.; Bensimon, C.;
Alper, H. Organometallics 1995, 14, 3927–3932. (b) Kas-
ka, W. C.; Nemeh, S.; Shirazi, A.; Potuznik, S. Organo-
metallics 1988, 7, 13–15.
(59) (a) Hanson, S. K.; Heinekey, D. M.; Goldberg, K. I. Or-
ganometallics 2008, 27, 1454-1463. (b) Kloek, S.; Hei-
nekey, D. M.; Goldberg, K. I. Angew. Chem., Int. Ed.
2007, 46, 4736–4738.
(60) (a) Boese, W. T.; Goldman, A. S. J. Am. Chem. Soc.
1992, 114, 350–351. (b) Maguire, J. A.; Boese, W. T.;
Goldman, M. E.; Goldman, A. S. Coord. Chem. Rev.
1990, 97, 179–192.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(65) Sakakura, T.; Tanaka, M. Chem. Lett. 1987, 16, 249–252.
(66) Kläui, W.; Schramm, D.; Peters, W. Eur. J. Inorg. Chem.
2001, 3113–3117.
(67) (a) Hasanayn, F.; Abu-El-Ez, D. Inorg. Chem. 2010, 49,
9162–9168. (b) Anderson, G. K.; Cross, R. J. Acc. Chem.
Res. 1984, 17, 67–74. (c) Calderazzo, F. Angew. Chem.,
Int. Ed. Engl. 1977, 16, 299–311. (d) Kuhlmann, E. J.; Al-
exander, J. J. Coord. Chem. Rev. 1980, 33, 195–225.
(68) Water contamination, or protic conditions, cause pro-
tonation of complex 3 to the aromatic cationic form
(complex 4a in the case of water), evident as a doublet
at 79.5 ppm (1JRhP = 120 Hz) in the 31P{1H}-NMR spec-
trum, which does not react at all under UV irradiation.
(69) Classic synthesis of benzaldehyde: Gattermann, L.;
Koch, J. A. Ber. Dtsch. Chem. Ges. 1897, 30, 1622–1624.
(70) Goikhman, R.; Milstein, D. Angew. Chem., Int. Ed.
2001, 40, 1119–1122.
(71) Although a catalytic process of benzene carbonylation
to benzaldehyde is thermodynamically uphill, further
hydrogenation of benzaldehyde to benzyl alcohol
would result in a close to thermoneutral process (CRC
Handbook of Chemistry and Physics, 96th ed., CRC
Press, Taylor and Francis group, LLC 2015) potentially
leading to a catalytically viable process of reductive
carbonylation of arenes.
(72) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb,
H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Gold-
berg, K. I. Organometallics 2010, 29, 2176–2179.
12
ACS Paragon Plus Environment